GTK: Fix autoc font size on GTK >= 3.21.0

GTK 3.21.0 fixed font size handling, leading to properly interpreting
pixels and points in CSS declarations.  However, as older versions
incorrectly handled those, the code has to handle both behaviours.

From CSS, GTK < 3.21.0 actually applied the conversion to points, but
incorrectly: 10px was used as 10pt, but 10pt was scaled up twice.

So, assuming 96 DPI, it leads to:

font-size | 3.20.0  | 3.21.0  |
----------|---------|---------|
10px      | 13.33px | 10px    |
10pt      | 17.77px | 13.33px |

So, we need to fix the code to accommodate for both (either scaling
ourselves, or adapting the unit: I chose the second, simpler, option).

See https://git.gnome.org/browse/gtk+/commit/?id=df08fc91bdc1d2e4c866122304fabe4dd298a7de

1 files changed, 9 insertions, 1 deletions

diff --git a/gtk/PlatGTK.cxx b/gtk/PlatGTK.cxx
index 74f095bc5..1629818ef 100644
--- a/gtk/PlatGTK.cxx
+++ b/gtk/PlatGTK.cxx
@@ -1494,7 +1494,15 @@ void ListBoxX::SetFont(Font &scint_font) {
 			ssFontSetting << "font-family: " << pango_font_description_get_family(pfd) <<  "; ";
 			ssFontSetting << "font-size:";
 			ssFontSetting << static_cast<double>(pango_font_description_get_size(pfd)) / PANGO_SCALE;
-			ssFontSetting << "px; ";
+			// On GTK < 3.21.0 the units are incorrectly parsed, so a font size in points
+			// need to use the "px" unit.  Normally we only get fonts in points here, so
+			// don't bother to handle the case the font is actually in pixels on < 3.21.0.
+			if (gtk_check_version(3, 21, 0) != NULL || // on < 3.21.0
+			    pango_font_description_get_size_is_absolute(pfd)) {
+				ssFontSetting << "px; ";
+			} else {
+				ssFontSetting << "pt; ";
+			}
 			ssFontSetting << "font-weight:"<< pango_font_description_get_weight(pfd) << "; ";
 			ssFontSetting << "}";
 			gtk_css_provider_load_from_data(GTK_CSS_PROVIDER(cssProvider),